Patent Document 1 to be indicated below discloses a synthetic resin container lid as a cap type synthetic resin container lid which can seal the mouth-neck section of a container sufficiently reliably, but can be removed from the mouth-neck section of the container without the use of an unsealing instrument. The synthetic resin container lid includes a circular top panel wall, a cylindrical skirt wall extending downward from the peripheral edge of the top panel wall and, in addition, a cylindrical restraint wall connected to the outer peripheral surface of the skirt wall via a breakable connecting section, and an operating section extending out downwardly beyond the skirt wall from the upper end of the operating section connected to the skirt wall. To mount the container lid on the mouth-neck section of the container, the skirt wall is fitted onto the mouth-neck section, and urged downward to bring an engagement ridge formed on the inner peripheral surface of the skirt wall into engagement with an engagement ridge formed on the outer peripheral surface of the mouth-neck section. Moreover, the restraint wall is urged downward with respect to the skirt wall, whereby the connecting section is broken to lower the restraint wall to such a state as to surround the skirt wall. To remove the container lid from the mouth-neck section of the container, thereby unsealing the mouth-neck section, the fingers are hooked over the operating section, and the operating section is urged radially outwardly and upwardly. By so doing, the restraint wall is partially displaced upward, and the skirt wall is partly displaced upward to remove the whole of the container lid from the mouth-neck section.